Experimental Hutch

Get detailed drawing of the Experimental hutch

The Troïka II diffractometer [8-circle diffractometer axis names] | [8-circle diffractometer sample stages] is a multi-purpose instrument which is optimized for scattering from surfaces and interfaces using grazing-incidence diffraction and reflectivity in both the horizontal and the vertical scattering geometry. The detector arm has both horizontal and vertical axes and can be equipped with various detectors.

The sample stages were designed to maximize the available volume for sample environments. The horizontal sample stage (see Huber 5202 stage in Figure 1) consists of a horizontal turn table, a height translation and crossed arcs. In combination with the deflector this stage has a six-circle or z-axis configuration. The horizontal stage is primarily used for scattering from liquid interfaces. Furthermore heavy sample environments up to 100 kg can be supported without counterweighting. A hemispherical volume of 450 mm diameter is available for sample environments. The sample position is 170 mm from the top of the crossed arcs. Optionally a xy-translation stage can be added on top of the arcs. In this case the sample position is 110 mm from the top of the xy-translation stage.

The vertical scattering stage (see Huber 5204 stage on Figure 1) comprises a vertical turntable and a long translation which permits the removal of this stage from the scattering position, if necessary. This stage is controlled by a 2+2 code (two detector axes and two sample axes). Additionally the sample goniometer has crossed arcs to line up the surface normal and two more translations. It can be used for small experimental set-ups of less than 2 kg and 250 mm diameter. The sample position is at 110 mm from the top plate of the crossed arcs.

Fig. 1: Schematic side view of the Troïka II diffractometer in the experimental hutch (see photo). The X-ray beam passes from right to left.

The detector arm has three possible configurations: The default configuration comprises an MicroControle X48 optical bench, motorized front slits, variable length flight path with Kapton windows and motorized detector slits. Either a scintillation detector or a Kapton detector can be used with this set-up. Alternatively the X48 bench can be equipped with a 150 mm Soller collimator of 1.4 mrad resolution and a 150 mm or 50 mm linear gas detector for the horizontal scattering configuration.

The second configuration consists of an analyzer stage. In horizontal scattering geometry a 150 mm Si(111) analyzer crystal can be combined with a 150 mm linear gas detector. In vertical scattering geometry various 50 mm analyzer crystals can be combined with a 50 mm linear gas detector.

The third configuration of the detector arm provides a mount for a MicroControle X95 profile which can be used for equipment that was originally designed for the Troïka I station. In this configuration X95 profile serves as a flightpath and a holder for collimation slits (JJ X-ray slits) and a detector.

The diffractometer can be equipped with a sealed Langmuir trough that is mounted on the top of active antivibrational system MOD-2 S fixed on horizontal stage. A conventional 2-circle analyser stage can be installed on detector arm.

The Experimental Hutch is air-conditioned and provides basic supplies (pressurised air and He gas from a bottle). A water purifying system is available on request. Simple sample-environment equipment and space for preparation of experiments is available in an adjacent laboratory.

Important information for planning of non standard experiments. Due to the small size of the experimental hatch, the maximum available length between center of the goniometer (sample position) and the wall is 940 mm.

Incident Flight Path

The incident flight path comprises optional upstream guard slits (GS), an evacuated tube with pneumatic filters inserter (XIA), down streem slits (S0), the incident beam monitor and an attenuator wheel close to the sample. The incident slits are motorized Huber slits using a home-build design that allows easy access and exchange of components. Motorized guard slits can be set-up at the entrance of the flight path for further collimation. The incident beam intensity is monitored by a scintillation detector, that stays at 90 deg to the beam and measures scattering from a thin 80mm Kapton foil. Variable apertures in front of the detector ranging from 0.5mm to 2mm allow the adjustment the of scattered photon flux to the dynamic range of the detector. The final optical element in the flight path is an attenuator wheel out of aluminum and consisting of 20 slots with absorber thickness ranging from 0 to 1.9mm in steps of 0.1mm. The attenuator has proven a very valuable tool in keeping the radiation dose onto sensitive organic samples to a minimum during line-up. Once grazing-incidence geometry is reached, the attenuation can be safely removed. Similarly, the detectors can be protected when lining up the sample on bulk Bragg reflections. Pneumatic filters inserter XIA (usually used with Al or Cu foils of different thickness) can be used additionally to the beam attenuation as a local shutter to protect sensitive samples from the X-ray beam on a time of motors motion between two points of acquisition.

Data Acquisition and Beamline Control

The beamline is controlled with MAXPC workstation. MAXPC is a PC under Linux and connected to the Ethernet. Stepping motors, encoders and detectors are driven or read out via a VME interface. Monochromator, deflector, and diffractometer are controlled by the SPEC software package from Certified Scientific Software. In horizontal scattering geometry the diffractometer can be positioned in six-circle mode or z-axis mode. For the vertical scattering geometry a 2+2 code can be used.

The present detector environment involves scintillation counters and two linear position sensitive detectors (PSD) (length: 50mm MBraun and 150 mm Gabriel/EMBL) with 150 µm spatial resolution both.

Basic data evaluation can be performed on a second terminal of the work station or on the beamline PC. Data from the workstation can be directly accessed from the PC. Some basic software for data analysis and commercial software packages are available on the workstation and on the PC.